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AK-toxin I, a host-specific toxin to Japanese pear (Pyrus serotina), was synthesized as its methyl ester from three precursor fragments: conjugated diene-carboxylic acid, chiral epoxyalcohol and β-methylphenylalanine. The epoxyalcohol fragment was derived from D-fructose, in which effective homologation of the hemiacetal carbon to alkyne by using dimethyl 1-diazo-2-oxopropylphosphonate was the key reaction. The diene-carboxylic acid fragment was prepared by repeated Wittig reactions, and was combined with the epoxyalcohol fragment by the Stille reaction. Esterification of the combined product with the stereochemically-pure β-methylphenylalanine fragment afforded the target compound. This method was used to prepare the methyl ester of tritium-labeled AK-toxin I with a specific radioactivity of 213 GBq/mmol.  相似文献   
2.
A bacterium R–4 which produces a novel type of lytic enzyme which lyses fungal and yeast cell walls was isolated from the air and was identified to belong to the genus Bacillus.

Production of the enzyme appeared to require a high concentration of nitrogen source in medium. No inducing substance was needed for the enzyme production.

A crude preparation of the enzyme was used to characterize the lytic activity. From the lytic spectrum, the enzyme seemed to have the highest activity toward the cell walls of species in the genus Rhizopus among various fungi and yeasts tested, A proteolytic activity was shown to be parallel with the lytic activity. The lytic activity was also accompanied with the liberation of reducing sugars from Rhizopus cell wall, but no activity on some known carbohydrates tested was detected in the preparation.  相似文献   
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